Bursaphelenchus cocophilus Scientific Name Bursaphelenchus cocophilus (Cobb, 1919) Baujard, 1989 Synonyms: Aphelenchoides cocophilus, Aphelenchus cocophilus, Chitinoaphelenchus cocophilus, Radinaphelenchus cocophilus, and Rhadinaphelenchus cocophilus. The red ring nematode, Bursaphelenchus cocophilus, was first described by Cobb (1919) as Aphelenchus cocophilus from specimens in Grenada. Since that time, it has undergone several name changes including the change to Rhadinaphelenchus cocophilus by Goodey (1960). This name is still commonly used within the scientific literature. Giblin-Davis et al. (1989b) presented morphological evidence supporting the similarities between Rhadinaphelenchus and Bursaphelenchus. Baujard (1989) synonymized the monotypic genus Rhadinaphelenchus with Bursaphelenchus creating the new combination, B. cocophilus. Molecular phylogenetic data presented by Ye et al. (2007) corroborates this synonymization. Common Name Red ring nematode, coconut palm nematode. Type of Pest Nematode Taxonomic Position Class: Secernentea, Order: Panagrolaimomorpha, Family: Aphelenchoididae Reason for Inclusion in Manual Palm commodity survey; national threat Pest Description Generalized Description: Females and males of B. cocophilus are 60 to 139 and 65 to 179 times longer than wide, respectively, with the greatest body width being less than 15.5 µm and total length ranging from 775 to 965 µm from little leaf symptomatic African oil palm and 812 to 1369 µm from coconut or African oil palms with typical red ring symptoms. The metacorpus and stylet in the second-stage juveniles and adults are well developed. Stylet length is between 11 to 15 µm in adults. Females have a vulval flap which appears bowed posteriorly when viewed ventrally, a long post-uterine sac (extending about 75% of the vulva-anal distance), and an elongate tail (62 to 117 µm) with a rounded terminus. Males have seven caudal papillae; one ventral preanal papilla, one pair of subventral preanal or adanal papillae, and two pairs of subventral postanal papillae. The distal ends of the spicules in the males are heavily sclerotized and the caudal alae form a spade-shaped flap. Third-stage dauer juveniles from coconut palm usually range from 700 to 920 µm and have a pointed tail with or without a Last updated: June 26, 2013 1 mucron. The metacorpus is usually not well developed in juveniles from the palm or the weevil vector and the stylet is not visible (Giblin-Davis et al., 2002). Juveniles: Juveniles (Fig. 1) have high, dome-shaped heads that are not offset from the body. The tails of the second- and third-stage juveniles are conoid with or without sharply mucronate tips. Those of fourth-stage juveniles have dimorphic tips: in female juveniles they are rounded as in the female, and in male juveniles are “sharply drawn out” (Dean, 1979). The third larval stage is 0.84 mm (0.03 in) and characterized by a tapered terminal end of the body (Brammer and Crow, 2002). Detailed Adult Descriptions from Dean (1979): Females (Fig. 1): Body about 1 mm [0.04 in] long and very slender, arcuate to nearly straight when relaxed; cuticle thin, marked with transverse striae, 0.6 to 1 μm apart. The lateral fields have four incisures that occupy 0.25 of the body width and a faint median line. The outer incisures are crenate. Deirids and phasmids are absent. The lip region is smooth, high, anteriorly flattened with rather straight sides, slightly narrower than and set off from the body. The head framework is prominent, sclerotized, a hexaradiate ribbed cylinder with sides forming fine bars which bifurcate basally. Spear/stylet is 11 to 13 µm long, attenuated, knobbed at the base and well developed. The stylet knobs may be obscure especially in immature specimens. The anterior part is less than half of the spear length and sharply pointed. The protractor muscles of the spear are prominent and attached to the basal plate of the labial framework. The procorpus is elongate to cylindrical. The metacorpus or median bulb is oval and usually about twice as long as wide with prominent valve plates just posterior to the center of the bulb. The dorsal oesophageal gland orifice is midway between the anterior margin of the bulb and the valve plate. Oesophageal glands overlapping the intestine dorsally and usually obscure. The nerve ring is a wide band surrounding the isthmus and about 0.5 to 1 bulb-length behind the bulb. The excretory pore a little behind the nerve ring and anterior to the hemizonid, which is about three annules long. Intestine has small granules and indistinct lumen. The vulva is slit-like and appears as an open C in ventral view, slightly overhung by a wide, thick dorsal lip. Posterior lip is also thick and heavily sclerotized. The vagina is thick-walled, slightly curved or distinctively C-shaped as it leads inwards to a distance of about 0.5 the body width. The ovary is well developed and outstretched with oocytes in a row. The postvulval uterine sac is elongate. The initial section has thickened walls probably representing part of the uterus, which extends about 0.75 the vulva-anus distance and serves as a spermatheca (often with a few large spheroid sperms). The rectum is about 1.5 anal body-widths long. The anus is distinct with an opening that is 0.25 to 0.5 that of the anal body width. The tail is elongate to subcylindrical with a rounded, unstriated terminus, 10 to 17 anal body- widths long (Dean, 1979). Males (Fig. 1): The body is about 1 mm long and very slender, ventrally arcuate, more strongly curved in the tail region. The head, stylet, and oesophagus as in the female. The testis is single, anteriorly outstretched to over 0.5 of the body length with spermatogonia in a row. Spicules are small, paired, and thorn-shaped. The dorsal limb is 9 to 13 µm long with an elongated rounded apex and ends dorsally before the ventral 2 limb whose distal ends appears to recurve to join the dorsal limb so that the entire spicule appears notched distally. The ventral element is 7 to 8 µm long, has a distinct rostrum proximally, and appears to be connected to the dorsal limb through a transverse bar with a central hole. There is no gubernaculum, but the dorsal wall of the spicule pouch is thickened to form an apophysis. The anus has an anterior lip protruding, posterior lip protruding, or both lips protruding. The tail is strongly curved ventrally, “0.8 to 1.5 of a circle” (Dean, 1979). It is subcylindrical in the anterior half, then conoid to a pointed terminus. Bursa (caudal alae) are short, terminal, and prominent in the dorsal or ventral view with finely striated margins. The bursa envelopes the distal 30 to 50% of the tail. There are a total of seven caudal papillae; a single ventral pre-anal papilla about 3 microns before the anus and an ad-anal pair followed by two pairs of distinct ventro-submedian papillae near the base of the bursa (Giblin-Davis et al., 1989). Biology and Ecology The life cycle of B. cocophilus lasts nine to ten days (Dean, 1979). The life cycle consists of an egg stage, four juvenile stages, and an adult stage (Chinchilla, 1991). The vector, Rhynchophorus palmarum (the South American palm weevil), deposits the dauer third stage juvenile of the nematode as it lays its eggs on palm leaf axils or internodes (Chinchilla, 1991; Giblin-Davis et al., 2002). B. cocophilus propagates in the host plant. Once the weevil eggs hatch, immature nematodes will enter the larvae, where they can remain while the weevils undergo metamorphosis. Once mature, the weevils will leave the host palm carrying dauer third-stage juvenile nematodes of B. Figure 1. Line drawings of B. cocophilus (cited as cocophilus with them to Rhadinaphelenchus cocophilus) from Dean (1979). 3 infect other host palms. B. cocophilus does not develop inside the weevil vectors. Adult weevils move B. cocophilus around by visiting infected host palms and either ingesting the nematode or carrying them on the surface of their bodies. B. cocophilus can sometimes be found in the tracheal sacs of the vector, where they can move to the ovipositor of females to be injected into host plant material (reviewed in Griffith et al., 2005). Only a few (10 to 50) nematodes are needed to cause disease when inoculated into a small wound (Griffith, 1968). Around five thousand nematodes, Figure 2. Cross-section of infected host palm. however, are needed for disease Characteristic red ring is visible as well as R. development on natural cracks or palmarum galleries (R. Giblin-Davis). coconut petioles (Griffith, 1968). Weevil vectors are attracted to palms with wounds or cuts in the trunks. Palms already infected and dying from red ring disease produce semiochemicals (kairomones) that are attractive to the weevil vectors (Giblin- Davis et al., 1996). B. cocophilus can survive long periods of time in nut husks (16 weeks), seedling tissue (90 weeks), and within the weevil. Dean (1979) states that B. cocophilus can survive in fresh water films for seven to eight Figure 3. Host palm showing chlorosis and wilting days and in sea water for three due to B. cocophilus (R. Giblin-Davis). days. B. cocophilus is susceptible to desiccation (Esser and Meredith, 1987). Griffith et al. (2005) states that, “the heaviest losses due to red ring disease occur at the end of the wet season and in the first two or three months of the dry season.” Low, poorly drained areas have the highest incidence of red ring disease; while drought conditions keep the disease in check (Esser and Meredith, 1987). The nematode survives best in wet, swampy areas and in clay rather than sandy soil. Possible root to 4 root transmission from trees infected with B.